The invention relates to a solution and concentrate for generating stable aqueous foams, and to a method of generating stable aqueous foams.
Stable high expansion aqueous foams have particular utility when used in security systems, i.e., as a dispensable deterrent for security systems, as visual obscurants because they increase the useful lifetime of the security system. More specifically, they are employed in security systems to prevent access to the unit to be protected by filling up a room to which access is to be prevented with the foams. Other uses of these foams include their use as foam drilling fluids for deep well drilling, as fire fighting agents, as well as other conventional uses which are well known to those skilled in the art.
Typically, the stability of high expansion aqueous foams is determined by measuring the liquid drainage from the foam. This is a measure of the density stability of the foam and is usually reported as the percent drainage at selected times. The present day foam systems in use in security systems give about 50% by weight drainage in 30 min.
The preferred foam systems generally have low solution viscosity so that the foam can be generated by conventional foam generating apparatus of the type wherein the foamable solution is sprayed on a perforated metal screen while blowing air through the screen. This device is conventional, and one example is illustrated in High Expansion Foam for Shipboard Firefighting, Fire Technology, vol. 5, 1969. Furthermore, it is desirable that a foam concentrate be storage stable, i.e., capable of being stored for long periods of time and still be effective for generating stable aqueous foams. The concentrate must also be easily mixable with water. However, up to now no system was known which provides all the above enumerated requirements. On the other hand, if a device capable of generating foams from gels is employed, when a low solution viscosity is not necessary. However, the present invention has special applicability to foam generating solution of low viscosity.